1. Field of the Invention
The present invention relates to a power amplifier using a power combiner, and more particularly to a power amplifier using a power combiner, which is capable of minimizing power loss and improving efficiency of the power amplifier with a large output power, by combining powers generated by a plurality of power amplifiers used in a wireless communication system using a transmission line transformer.
2. Description of the Related Art
A power combiner and a power amplifier are used for allowing a transmitter of a wireless communication system to transmit a radio frequency signal with a large output power.
FIG. 1 is a view showing the configuration of a general power amplifier.
As shown in FIG. 1, the power amplifier includes an amplifier unit including a power transistor 101 and a matching circuit 102 for converting a value of a load resistor connected to an output port 103 into a value of a load resistor for allowing the power transistor 101 to generate a large power.
In general, in a wireless communication system, the value of the load resistor connected to the output port 103 is 50Ω, but a value Rload_optimum is not 50Ω. Accordingly, the matching circuit 102 is required.
In order to obtain an output power larger than that of the power amplifier shown in FIG. 1, an amplifier unit larger than the power transistor 101 is required.
FIG. 2 is a view showing the structure of a general amplifier for generating a large output power using several amplifiers.
In FIG. 2, an amplifier unit 201 includes several power transistors 101 so as to generate an output power larger than that of the power transistor 101.
As shown in FIG. 2, in the general power amplifier, the output powers generated by the amplifier unit 201 are combined by a power combiner and a matching circuit 202. At this time, the powers should be combined by the matching circuit 202 such that power loss is minimized.
In general, the matching circuit 202 includes a combination of passive elements such as an inductor or a capacitor.
However, since such passive elements formed on a silicon substrate having an integrated CMOS have a large parasitic resistance component, large power loss is generated in the power combiner and the matching circuit 202.
If a power amplifier for generating an output power of several Watts is formed on the silicon substrate in a current technological level, the power loss generated in the power combiner and the matching circuit reaches 50% of the power generated in the power transistor.
Accordingly, in the current technological level, a power amplifier obtained by integrating all passive elements on a silicon substrate is negligibly commercialized.
In order to overcome such a problem, in most of current power amplifiers, passive elements are made of a compound semiconductor having a small parasitic resistance component or are implemented on an off-chip without being integrated. However, such a method increases manufacturing cost of a power amplifier.